Prior to the present invention, various one and two-package moisture curable room temperature vulcanizable (RTV) compositions were available based on the use of a silanol-terminated polydiorganosiloxane having the formula, ##STR1## where R is a C.sub.(1-13) monovalent substituted or unsubstituted hydrocarbon radical, which is preferably methyl, or a mixture of a major amount of methyl and a minor amount of phenyl, cyanoethyl, trifluoropropyl, vinyl, hydrogen and mixtures thereof, and n is an integer having a value of from about 50 to about 2500, with a cross-linking silane having hydrolyzable radicals attached to silicon.
For example, Ceyzeriat, U.S. Pat. No. 3,133,891 and Bruner, U.S. Pat. No. 3,035,016, are based on the use of methyltriacetoxysilane with a silanol-terminated polydimethylsiloxane under substantially anhydrous conditions. Although the one-package compositions of Bruner or Ceyzeriat, upon exposure to atmospheric moisture, provide satisfactory one-package room temperature vulcanizable organopolysiloxane compositions exhibiting satisfactory tack-free time, for example, 30 minutes or less after an extended shelf period, the acetic acid by-product is corrosive and has a disagreeable odor. Other variations of one-package acyloxy acid generating RTV's are shown by Kulpa, U.S. Pat. No. 3,296,161, Goossens, U.S. Pat. No. 3,296,195 and Beers, U.S. Pat. No. 3,438,930, assigned to the same assignee as the present invention. Additional one-package acyloxy acid generating RTV compositions are shown by Schulz et al, U.S. Pat. No. 3,647,917 and Nitzsche et al U.S. Pat. No. 3,886,118.
An improved, low odor, substantially non-corrosive one-package RTV composition is shown by Beers, U.S. Pat. No. 4,257,932, assigned to the same assignee as the present invention. Beers achieves a reduction in odor and corrosive properties by utilizing as a cross-linking silane a less volatile material such as methyltris-(2-ethylhexanoxy)silane.
A non-corrosive two package moisture curable organopolysiloxane composition free of carboxylic acid generating groups is shown by Nitzsche et al, U.S. Pat. No. 3,127,363 which is based on the use of a polyalkoxysilane, or polysilicate cross linking agent, in place of methyltriacetoxysilane. The ingredients of the two package non-corrosive composition of Nitzsche et al, are mixed under atmospheric conditions and the resulting composition must be used soon after the ingredients are mixed because the resulting blend has a short shelf life. Although the mixture of Nitzsche et al, which is typically polyalkoxysilane, silanol-terminated polydiorganosiloxane and tin soap catalyst, provides upon mixing, a fast curing non-corrosive room temperature vulcanizable composition, the Nitzsche et al mixture does not have the extended shelf life advantage of the one-package system which is required for commercial use and therefore is excluded from a variety of applications.
Nitzsche et al, U.S. Pat. No. 3,065,194, teaches that a mixture of an endblocked dimethylsiloxane polymer, such as hydroxy and alkoxy endblocked, inert filler, ethylorthosilicate and dibutyltindilaurate can be vulcanized upon contact with water, after a 14 day shelf period at room temperature. However, the various ingredients of the mixture have to be vigorously dried by heating for 1 hour at 200.degree. C., and the RTV, after a relatively short shelf period, has to be drenched with water.
Improved results toward combining the advantages of a non-corrosive acid-free polyalkoxysilane cross-linking agent with a silanol-terminated polydiorganosiloxane as a one-package system are shown by Weyenberg, U.S. Pat. No. 3,334,067, Cooper et al, U.S. Pat. No. 3,542,901 and by Smith et al, U.S. Pat. Nos. 3,689,454, and 3,779,986, the last two being assigned to the same assignee as the present invention, utilizing a titanium chelate catalyst in place of a tin catalyst. However, after room temperature vulcanizable one-package systems based on a titanium chelate catalyst were allowed to age for a period of 5 hours or more, it was found that the tack-free time of the aged RTV was considerably longer than the tack-free time of the same mixture after it was initially mixed and immediately exposed to atmospheric moisture.
As shown by Brown et al U.S. Pat. No. 3,122,522, a platinum catalyst is used to prepare an alkoxy terminated silalkylenepolysiloxane polymer. However, this method of synthesizing the base polymer requires an expensive hydrosilylation procedure. Additional efforts to achieve a desirable non-corrosive, substantially odor-free stable one-package RTV based on the use of polyalkoxyorganopolysiloxane in a more economic manner are shown by Brown et al, U.S. Pat. No. 3,151,514 or U.S. Pat. No. Re. 29,760. Brown et al employed a polyalkoxy end blocked polysiloxane which was based on the use of a mineral acid generating polyalkoxyhalosilane, and a curing catalyst. However, these compositions were found to be unusable because they failed to cure in contact with a tin catalyst, even in the presence of moisture.
As utilized hereinafter, the term "stable" as applied to the one-package polyalkoxy-terminated organopolysiloxane RTV's of the present invention means a moisture curable mixture capable of remaining substantially unchanged while excluded from atmospheric moisture and cures to a tack-free elastomer after an extended shelf period.
The present invention is based on the discovery that stable, substantially acid-free, one-package, moisture curable organopolysiloxane RTV compositions can be made by using an aluminum complex having the formula EQU (G).sub.a Al(Q).sub.3-a ( 2)
as a condensation catalyst with silanol terminated, or alkoxy terminated polydiorganosiloxane, in place of tin compounds or titanium chelates as previously discussed, where G is a monovalent radical selected from the class consisting of --OR.sup.1, --OSi(R.sup.1).sub.3, --N(R.sup.1).sub.2 and --SR.sup.1, R.sup.1 is a monovalent radical selected from C.sub.(1-13) hydrocarbon radicals and substituted hydrocarbon radicals, or G can be a divalent radical of the formula, EQU --D--Z--D--,
D is a divalent radical selected from --O--, --N-- and --S-- and mixtures thereof, Z is a divalent radical selected from C.sub.(6-13) arylene and C.sub.(1-8) alkylene, and when D is --O--, Z also can be ##STR2## where b has a value of 0 to 5 inclusive, Q is a monovalent anion selected from ##STR3## Z.sup.1 is a divalent radical selected from C.sub.(6-13) aromatic hydrocarbon radicals, and substituted C.sub.(6-13) aromatic hydrocarbon radicals, R.sup.2 and R.sup.3 are the same or different monovalent radicals selected from hydrogen, R.sup.1, -OR.sup.1, OSi(R.sup.1).sub.3, acyl and nitrile R.sup.4 is a monovalent radical selected from hydrogen, R.sup.1 and OR.sup.1 and a is a whole number equal to 0 to 3 inclusive.
The cross-linking polyalkoxysilane which can be utilized in combination with the above-described aluminum complex of the present invention and the silanol terminated or alkoxy terminated polydiorganosiloxane has the formula, ##STR4## where R.sup.1 is as previously defined, R.sup.5 is a C.sub.(1-8) aliphatic organic radical selected from alkyl radicals, alkylether radicals, alkylester radicals, alkylketone radicals and alkylcyano or a C.sub.(7-13) aralkyl radical and c is a whole number equal to 0 or 1.
Polyalkoxy terminated organopolysiloxane which can be used to make the RTV compositions of the present invention has the formula, ##STR5## where R, R.sup.1, R.sup.5, and n are as previously defined and d is a whole number equal to 0 to 2 inclusive. The polyalkoxy terminated organopolysiloxane of formula (4) can be made by various procedures. One procedure is taught by Cooper et al U.S. Pat. No. 3,542,901 involving the use of a polyalkoxysilane with a silanol-terminated polydiorganosiloxane in the presence of an amine catalyst. A second procedure is shown in the copending application of Mary Ann White et al, Ser. No. 277,524, filed June 26, 1981, now U.S. Pat. No. 4,395,526, utilizing an alkoxy silane scavenger as an end-capper with silanol terminated polydiorganosiloxane of formula (1). Another procedure is shown in my copending application RD-14595 Ser. No. 520,978 utilizing silanol terminated polydiorganosiloxane of formula (1), polyalkoxysilane of formula (3) and an effective amount of the aluminum complex of formula (2).
It has been further found that improved cure rates can be achieved if minor amounts of amines, substituted guanidines, or mixtures thereof, are utilized as curing accelerators in the polyalkoxy compositions of the present invention. There can be used from 0.1 to 5 parts, and preferably from about 0.3 to 1 part of curing accelerator, per 100 parts of the silanol-terminated polymer of formula (1), or 100 parts of the polyalkoxy-terminated polymer of formula (4) to substantially reduce the tack-free time (TFT) of the RTV composition of the present invention. This enhanced cure rate is maintained after it has been aged for an extended shelf period, for example, 6 months or more at ambient temperatures, or a comparable period under accelerated aging conditions. Its cure properties after the extended shelf period will be substantially similar to its initial cure properties, for example, tack-free time (TFT), shown by the RTV composition upon being freshly mixed and immediately exposed to atmospheric moisture.